Ethanol is the most widely used liquid biofuel in the world. In the U.S., ethanol is typically used as a gasoline additive and is blended into gasoline at up to 10 percent by volume to produce a fuel called E10 or “gasohol.” In 2005, total U.S. ethanol production alone was 3.9 billion gallons, or 2.9 percent of the total gasoline pool. In 2006, that number increased to 4.86 billion gallons, and is well on pace to further rise in 2007. Therefore, the efficient and inexpensive production of materials to produce ethanol is of great interest.
One source of feedstock material to produce ethanol is soluble sugars produced by hydrolyzing cellulose. Such hydrolysis processes currently draw significant interest because large amounts of cellulosic feedstocks, such as biomass materials, can be easily and cheaply obtained, and environmentally, the burning or landfilling of waste cellulosic materials can be reduced. Exemplary types of biomass materials include switchgrass, wood, paper, agricultural residues, industrial solid wastes, and herbaceous crops. The hydrolysis processes are characterized by the breaking of the bonds between the glucose monomer units of cellulose to provide soluble sugar moieties, which are fermentable into ethanol.
Two hydrolysis methods are commonly used: acid hydrolysis and enzymatic hydrolysis. However, neither process is optimal. Acid hydrolysis can be performed with dilute or concentrated acid. Unfortunately, dilute acids require high temperature and pressures while concentrated acids must be removed from the product before fermentation can occur. On the other hand, enzymatic processes require a stable supply of enzymes and pretreatment to more easily hydrolyze the cellulose, especially with lignocellulosic material. Also, as set forth in U.S. Pat. Nos. 6,419,788 and 4,461,648, for example, because of the complex chemical structure of lignocellulosic material, which includes lignin and hemicellulose that coat the cellulose, microorganisms and enzymes cannot effectively attack the cellulose without prior treatment because the cellulose is highly inaccessible to enzymes or bacteria. Accordingly, there is a need for a more efficient and inexpensive method of producing fermentable sugars for the mass production of ethanol.